Former premier Tun Dr Mahathir Mohamad is celebrating his 90th birthday today, but there's no sign that he is slowing down, even the slightest bit, especially in his comments and opinions on national issues.

Dr Mahathir, who was Malaysia's fourth prime minister, has always been and is still very outspoken on matters that bothers him -- be it political, financial or personal matters. His opinions command much attention, positive and negative alike.

The Kedahan who helmed the country for 22 years from 1981 to 2003, is now often seen as one of the harshest critics of the 1Malaysia Development Berhad (1MDB) scandal and Prime Minister Datuk Seri Najib Razak.

It is learned that the UMNO stalwart will be having a big birthday celebration this month.

Meanwhile, his daughter, Datin Paduka Marina Mahathir, took to her social network pages to wish her 'daddy' a happy birthday.

In her message, she wished Dr Mahathir the strength and courage to do what he thinks is right.

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His granddaughter, Meera Alyanna Mukhriz, posted a picture of her grandfather’s birthday celebration on her Instagram page, wishing him 'Selamat Hari Lahir Tok Det'.

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In Twitter, messages for the much adored former premier came in dozens under the hashtag #TunM90

Here are some of the wishes: